Timepieces including devices for providing this power reserve indication are devised to take account of the rotation of the ratchet wheel during winding of the barrel spring and the rotation of the barrel when the barrel spring is let down. In order to do this, most of these known devices implement a differential gear. A device of this type is disclosed, for example, in EP Patent No. 1 074 897 wherein the two differential inputs are respectively connected to the toothing of the barrel drum and to that of the ratchet wheel, the differential gear output being connected to an indicator member.
In order to display the number of barrel spring winding turns, which is generally of the order of 10 for barrels with a power reserve of the order of 2 days, using an indicator member of the type moving opposite a scale extending at the very most over 360°, reduction wheels have to be associated with the different gear. These reduction gears are typically arranged between the drum barrel and the first differential gear input, between the ratchet wheel and the second differential gear input and between the differential gear output and the indicator member. The presence of these reduction gears is ill suited to an advantageous embodiment is some specific cases, particularly when the movement includes numerous complications multiplying the number of parts and that space available around the barrel is relative limited. Moreover, the inherent construction clearances present in these reduction gears lead to inaccuracies in the power reserve display. These display inaccuracies are greater the greater the arc along which the power reserve indication is displayed.
There is also known from DE Utility Model No. 1638800U a power reserve indicator using a plane differential gear with a double satellite wheel arranged between the barrel bar and the barrel cover for the purpose of omitting the winding and let down reduction trains. However, the reduction ratio offered by this type of differential gear does not allow the power reserve to be displayed over a small arc of a circle, for example of the order of 30° without a display reduction train. Moreover, although this power reserve device is compact horizontally, it has a significant space requirement heightwise, which impedes the use thereof in movements of small thickness.
It is an object of the present invention to overcome the aforementioned problems and drawbacks, in addition to others, by proposing a timepiece including a power reserve indicator that is compact horizontally and heightwise and is of very simple construction, while creating a more judicious arrangement of the power reserve indicator device elements.
It is another object of the invention to provide a timepiece including a power reserve indicator device that limits or omits the winding, let down and power reserve display reduction trains.
It is another object of the invention to provide a timepiece including a power reserve indicator device with improved power reserve display accuracy.
It is yet another object of the invention to provide a timepiece including a power reserve indicator device that can display the power reserve over an arc of a circle of less than 30° without any reduction trains.